The persistent internet joke claiming Borzois have "flexible" muzzles comes from a funny quirk of soft-tissue mechanics. While the maxillary and nasal bones are rigid, the external structures around the snout are unusually loose.
A Borzoi possesses elastic lateral cartilages at the tip of the nares, surrounded by long, dry flews (lips) that lack the heavy padding found in mastiffs. When a Borzoi presses its face against a window, squeezes through a baby gate, or rests its chin on a couch arm, the bony ridge stays straight while the soft tissue, skin, and whisker pads slide sideways.
Because the skull is so slender, this skin movement stands out immediately. If a Labrador leans its face on glass, broad cheek muscles keep everything in place. When a Borzoi does the same, the lack of lateral skull width lets the nose pad pivot relative to the jawline. The dog looks like someone grabbed the end of a sock and twisted it thirty degrees to the left. The hound feels no discomfort; its skin is simply adapting over a blade-thin skull.
